The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device which is called In-Plane Switching Mode.
Liquid crystal display device which is called In-Plane Switching Mode has a construction in which a pixel electrode and a counter electrode which causes an electric field (an in-plane electric field) having a component parallel to transparent substrates to be generated between the counter electrode and the pixel electrode are formed in each liquid crystal-side pixel area of one of the transparent substrates disposed in opposition to each other with a liquid crystal interposed therebetween.
This type of liquid crystal display device is constructed so that the amount of light to be transmitted through the area between the pixel electrode and the counter electrode is controlled by the driving of the liquid crystal to which the electric field is applied.
Such a liquid crystal display device is known as a type which is superior in so-called viewing angle characteristics and enables a displayed image to be unchanged even when its display surface is observed from an oblique direction.
The pixel electrode and the counter electrode have so far been formed of a metal layer which does not transmit light therethrough.
In recent years, a liquid crystal display device constructed in the following manner has been known: a counter electrode made of a transparent electrode is formed over the entire area of a pixel area except the periphery thereof, and strip-shaped pixel electrodes are formed on the counter electrode with an insulating film interposed therebetween, in such a manner as to be extended in one direction and to be juxtaposed in a direction traverse to the one direction.
The liquid crystal display device having this construction causes an in-plane electric field to be generated between each of the pixel electrodes and the counter electrode, and is still superior in viewing angle characteristics and is greatly improved in aperture ratio.
Incidentally, this art is described, for example, in SID (Society for Information Display) 99 DIGEST: pp. 202-205 and Japanese Patent Laid-Open No. 202356/1999, which is incorporated herein by reference.
However, in the liquid crystal display device having this construction, the occurrence of so-called horizontal smear is visually observed on its display portion, and the occurrence of image retention is also visually observed.
It has been found out that the cause of the occurrence of horizontal smear is that the capacitance between the counter electrode formed over the entire area of the pixel area except the periphery thereof and the plural strip-shaped pixel electrodes formed in juxtaposition on the counter electrode with the insulating film interposed therebetween becomes larger than in previous type and the charge of the pixel electrodes with signal voltages becomes insufficient, and also the voltage of the counter electrode is distorted and the time required for the distorted voltage to be restored to its original state becomes long.
It has also been found out that the cause of the occurrence of image retention is that an electric field other than an electric field which has a component parallel to the substrate between the pixel electrode and the counter electrode and contributes to the control of the optical transmissivity of the liquid crystal, i.e., an electric field having a component perpendicular to the substrate between the counter electrode and the pixel electrode, is excessively strong.